The invention concerns a blind-stitch sewing machine having a fabric bender to bulge the material to be sewn into the arcuate path of a sewing needle.
Such blind-stitching machines having plate-shaped fabric benders are known as represented by U.S. Pat. No. 2,355,904 and German Offenlegungsschrift 20 37 502. In these prior arrangements, the fabric bender is rotatably supported approximately at its center or at an end and is loaded by a tension or compression spring in a direction away from a solid drive shaft for the fabric bender. The drive shaft is rotatably supported in a fabric-support arm of the blind-stitching machine and during sewing pivots to-and-from in synchronization with the to-and-fro pivoting arc needle of the machine and with a correspondingly timed stepwise advance of the sewing material. The fabric bender is received in a slot of a support assembly projecting perpendicularly from the drive shaft, which slot extends transverse to the drive shaft in an end of the support assembly remote from the drive shaft.
The tension spring is extended between an end of the centrally supported fabric bender and an arm of the support assembly. This arm and the support assembly are radial to the drive shaft. The tension spring forces the fabric bender against the bottom of the slot in the support assembly. From this position the fabric bender can pivot against the force of the tension spring while its other end moves away from the path of the arc needle toward the drive shaft of the fabric bender. During sewing, when a thicker portion of the sewing material arrives near the fabric bender, a sewing-material sensor causes the pivoting of the fabric bender. The sewing-material sensor takes the form of a lateral stud secured to the other end of the fabric bender and contacts the sewing material on one side of the bulge formed therein by the fabric bender.
The compression spring is mounted in a longitudinal borehole of the support assembly and rests at one end on an adjustment screw threadable into the borehole to change the bias of the compression spring and at the other end through a ball on that end of the fabric bender which is remote from its pivot axis. To limit the range within which the fabric bender can be pivoted inside the slot, the support assembly comprises a stop pin extending transversely in the slot through an elongated and arcuate hole in the fabric bender that is concentric with the pivot axis of the fabric bender. The compression spring urges the fabric bender against the stop pin. The fabric bender can pivot from this position against the force of the compression spring until the other end of its elongated hole contacts the stop pin, the end of the fabric bender which is near the compression spring moving away from the path of the arc needle toward the drive shaft of the fabric bender. The fabric bender pivots to leave the first-stated position whenever, during sewing, a thicker sewing material portion arrives between the fabric bender and a stop at a throat plate of the blind-stitching machine. The fabric bender makes the sewing material bulge against the stop which is spring-loaded toward the sewing material so the stop will yield and move against the spring action by an amount which can be adjusted by means of an adjustment screw.
Moreover, blind-stitching machines are known having such a fabric bender urged by means of a compression spring into the normal position in a support assembly and cooperating with a stop similar to the one discussed above, and further comprising a second, also plate-shaped fabric bender pivoting to-and-fro which, however, is rigidly joined to its associated drive shaft and cooperates with a stop located at the throat plate of the blind-stitching machine which is spring-loaded toward the sewing material but not adjustable with respect to the amount of yielding. The two fabric benders are mounted next to each other and alternatingly make the sewing material bulge, each against the associated stop. This type of blind-stitching machine is described in U.S. Pat. No. 3,747,546.
In another known arrangement, as shown in U.K. Pat. No. 1,331,476, two bar-shaped fabric benders can be shifted axially to-and-fro by means of an associated drive shaft. Each fabric bender in this arrangement is elastically supported through a compression spring in a bushing connected to the drive shaft. The bias of the compression spring is adjustable by means of an adjustment screw. The drive shaft of one of the fabric benders is hollow and rotably supported on the drive shaft of the other fabric bender which, in turn, is rotatably supported in a fabric-support arm of the blind-stitching machine. This fabric-support arm is spring-loaded into the sewing position to abut a stop whose position can be adjusted by means of an adjustment screw through a linkage to change the distance between the fabric-support arm in the sewing position and the path of the blind-stitching machine arc needle, i.e. to adjust the stitch-depth of the arc needle in the sewing material made to bulge by the fabric benders. The two fabric benders make the sewing material bulge against a common stop mounted on a throat plate of the blind-stitching machine. The common stop is spring-biased toward the sewing material in order to be able to yield and to move against the spring action by an amount determined by the position of an adjustment screw.